Population based hospitalization burden of laboratory-confirmed hand, foot and mouth disease caused by multiple enterovirus serotypes in Southern China

Preclinical safety evaluation of a bivalent inactivated EV71-CA16 vaccine in mice immunized intradermally

Hand, foot and mouth disease is a common acute viral infectious disease that poses a serious threat to the life and health of young children. With the development of an effective inactivated EV71 vaccine, CA16 has become the main pathogen causing HFMD. Effective and safe vaccines against this disease are urgently needed. In our previous study, a bivalent inactivated vaccine was shown to have good immunogenicity and to induce neutralizing antibodies in mice and monkeys. Repeated administration toxicity is a critical safety test in the preclinical evaluation of vaccines. In this study, BALB/c mice were used to evaluate the toxicity of the bivalent vaccine after multiple intradermal administrations. Clinical observation was performed daily, and body weight, food intake, hematological characteristics, serum biochemical parameters, antinuclear antibodies, CD4⁺/CD8a⁺ T-cell proportions, bone marrow smear results and pathology results were recorded. The results showed that there was no significant change at the injection site and no adverse reactions related to the vaccine. The bivalent inactivated EV71-CA16 vaccine exhibits good safety in mice, and these results provide a sufficient basis for further clinical trials.

Experimental animal models for development of human enterovirus vaccine

Enterovirus infections induce infectious diseases in young children, such as hand, foot, and mouth disease which is characterized by highly contagious rashes or blisters around the hands, feet, buttocks, and mouth. This predominantly arises from enterovirus A71 or coxsackievirus A16 infections and in severe cases, they can lead to encephalitis, paralysis, pulmonary edema, or even fatality, representing a global health threat. Due to the absence of effective therapeutic strategies for these infections, various experimental animal models are being investigated for the development of vaccines. During the early stages of research on enterovirus infections, non-human primate infections exhibited symptoms like those in humans, leading to their utilization as model animals. However, due to economic and ethical considerations, their current usage is limited. While enterovirus infections do not readily occur in mice, an infection model with mouse-adapted strain in neonatal mice has been employed. Cellular receptors have been identified in human cells, and genetically modified mice expressing these receptors have been used. Most recently, the utilization of Mongolian gerbil model is actively being considered and should be pursued for further animal model development. So, herein, we provide a summarized overview of the current portfolio of available enterovirus infection models, emphasizing their respective advantages and limitations.

Seroepidemiology of enterovirus A71 infection in prospective cohort studies of children in southern China, 2013-2018

Enterovirus A71 (EV-A71)-related hand, foot, and mouth disease (HFMD) imposes a substantial clinical burden in the Asia Pacific region. To inform policy on the introduction of the EV-A71 vaccine into the National Immunization Programme, we investigated the seroepidemiological characteristics of EV-A71 in two prospective cohorts of children in southern China conducted between 2013 and 2018. Our results show that maternal antibody titres declined rapidly in neonates, with over half becoming susceptible to EV-A71 at 1 month of age. Between 6 months and 2 years of age, over 80% of study participants were susceptible, while one third remained susceptible at 5 years old. The highest incidence of EV-A71 infections was observed in children aged 5-6 months. Our findings support EV-A71 vaccination before 6 months for birth cohorts in southern China, potentially with a one-time catch-up vaccination for children 6 months-5 years old. More regionally representative longitudinal seroepidemiological studies are needed to further validate these findings.

Immunogenicity and safety of the inactivated enterovirus 71 vaccine administered concomitantly with the measles-rubella vaccine in infants aged 8 months in China: A noninferiority randomized controlled trial

BACKGROUND

To evaluate the immunogenicity and safety of simultaneous administration of the enterovirus 71 (EV71) vaccine with the measles and rubella (MR) combined vaccine.

METHODS

In this phase 4, randomized, open-label and noninferiority study, a total of 680 infants aged 8 months were enrolled and assigned to the simultaneous administration group (infants received the first dose of EV71 vaccine and MR vaccine on Day 0, and the second dose of EV71 vaccine on Day 28), or the separate administration groups (EV71 group: infants received two doses of EV71 vaccine on Day 0 and Day 28, respectively; MR group: infants received MR vaccine on Day 0). Blood sample was obtained on Day 0 and Day 56 to measure antibody responses to each of the antigens in terms of antibody titer or concentration, respectively. Local and systemic adverse reactions (ARs) and other adverse events (AEs) following each dose were monitored and compared among groups.

RESULTS

After vaccination, simultaneous administration group showed similar seroconversion rates of antibody against EV71(97.9%), measles (97.4%), and rubella (94.3%) compared to EV71 group (99.6% for anti-EV71) or MR group (98.4% for anti-measles and 98.9% for anti-rubella, respectively). Noninferiority was demonstrated for all antibodies as the lower limits of two-sided 97.5% confidence intervals (CIs) of the difference in seroconversion rates between simultaneous administration group and separate administration groups were above the predefined margin of -10%. Additionally, the adverse reaction rates were comparable among groups (54.4% in the simultaneous group versus 43.9% in the MR group versus 52.6% in the EV71 group).

CONCLUSION

Antibody responses induced by simultaneous administration of EV71 vaccine with MR vaccine were robust and noninferior to those by single administration alone. Like the previous findings by single administration alone, simultaneous administration demonstrated comparable reactogenicity and safety profiles.

Efficacy of an inactivated bivalent vaccine for enterovirus 71 and coxsackievirus A16 in mice immunized intradermally

Human hand, foot, and mouth disease (HFMD), an important infectious disease in children, is caused mainly by enterovirus 71 (EV71) and coxsackievirus A16 (CA16). In this study, a bivalent inactivated EV71/CA16 vaccine is developed and evaluated in immunized BALB/c mice injected through the intradermal route. Q-RT-PCR detection of the mRNA of immune signal molecules in local epithelial tissues inoculated with the vaccine indicates activation of innate immunity, which includes upregulation of immune-related chemokines, interferons and CD molecules. Further, the finding that neutralizing antibodies and specific T cellular responses were elicited in adult mice after two immunizations with the vaccine at a 28-day interval, which endowed offspring mice to defend a viral challenge, suggests the successful induction of specific protective antiviral immunity. All these data suggest that immunization with this bivalent EV71/CA16 vaccine via the intradermal route elicits effective immunity against EV71 and CA16 infection.